The best solution is to run your own mail server. A few of your emails will probably still be rejected by the recipient ISP's ("We don't accept emails from dynamic IPs), but most of them will get through. I know this because I wrote a mass email script for sending bulletins to homeschool groups listed on my parents' web site.

Just be sure to NOT send the same email twice, especially not to the same address. This will get you on the spam lists real fast.